Electric heating unit



May 4 c. c. ABBOTT ELECTRIC HEATING UNIT Original Filed April 4 19?.2

Im/enbov: Charles Cflbbofb'b,

b5 MM His Jq-b-bor-hey.

. Patented May 2t), 1924.

UNITED ST TE 1,494,938 PATENT OFFICE.

CHARLES C. ABBOTT, OF PITTSFIELD, IASSACHUSETTS, 'ASSIGNOB TO GENERAL ELECTRIC COMPANY, A CORPORATION 01 NEW YORK.

ELECTRIC HEATING- UNIT.

Application filed April 4, 1922, Serial 1W0. 549,638. Renewed February 12, 1924,

To all whom. it may concern:

Be it known that I, Cams 0. Anno'r'r, a citizen of the United States, residing. at Pittsfield, in the county of Berkshire, State 6 of Massachusetts, have invented certain new and useful Improvements in Electric Heating Units, of which the following is a specification.

My invention relates to electric heating I 10 units and has for its object the provision of improvements in electric heating units.

More specifically my invention relates to sheath wire heating units of the type con- 7 sisting of a resistance conductor embedded in a compacted mass of insulating material enclosed by a metallic sheath, although it may obviousl be applied to various other types of heating units. Certain features of my present inventionare disclosed in my copending, application, Serial No. 505,588,

filed October 5, 1921, of which this application is a continuation in part. In sheath wir heating units, it is desirable to provide a terminal for the resistance conductor made of a suitably hard metallic material,

adapted to withstand theswaging operation to which the unit is subjected. This terminal projects from the sheath where a connecting lu made of a suitably soft electrically .con 'ucting material, such as brass,

may be secured to it to facilitate the connection of leads from the source of electri-' cal supply.

In carrying out my invention I have provided a simple and reliable electrical connection between the terminal and the res'istance conductor which can be made without the use of a brazed joint I have also provided means whereby the connecting lug 40 may be quickly and rigidly secured to the end of the terminal and whereby the heating unit may be sealed with the same operation. In one form of my invention I provide threads on one end of the terminal and'secure a helical resistance conductor thereto by screwing it on the threaded portion. In securing the connecting lug to the terminal I provide nicks in the projecting portion of the terminal, the nicked portion being inserted in a'recess in the lug, and the lug then being compressed so. as to force the metal into the nicks and also elongate the lug wherebyit is seated tightly against an insulating washer closing the end of the heating wnit.v

For a more complete understanding of my invention reference should be had to the accompanying drawing in which Fig. 1 is a view showing a terminal embodying my invention; Fig. 2 is a view partially in sec tlon showing the terminal assembled in the heating unit before the swaging operation;

Fig. 3 is a section along the line 3-3 of 11, the threads of which are flattened at the bottom, and with a cylindrical pointed extension 12 having a diameter equal to or slightly less than the diameter of port-ion 11 'at the bottom of the threads. Adjacent the threaded portion is a shoulder 13. The. opposite end of the terminal is provided with an annular groove 15.

In assembling the heating unit in accordance with my invention, a triangular mica spacing washer 16 is placed on shoulder 13.- and'a helical resistance conductor 17 turned or screwed on the threaded portion 11, the diameter of .the helix being slightly less than the diameter of the terminal at the root of the threads so that the helix is expanded somewhat. The resistance conductor. consequently contracts by reason of its resiliency on the threaded portion making a good electrical connection. It will be observed that any force tending tounscrew the re sistanceconductor from the terminal will furthertighten or contract it on the threaded portion thus effectively preventing its removal. Very simple and efiicient electrical connection is thus provided. The cylindrical extension 12 tends to straighten out the helix of the resistance conductor and prevent any possibility of the turnsgetting across the threads.

A terminal is secured in this manner to each end of the resistance conductor, and the resistance conductor with the two terminals attached is then inserted in a metallic sheath 18, as shown in Fig. 2. The'outer 'endof the terminal 10 is held in place centrally of the sheath by means of a star washer 19 in serted in the end of the sheath around the terminal, the sheath preferably being countersunk to receive the washer. A clip 20 placed in groove 15 engages the star washer so as to hold the terminal against longitudinal movement from the tension of the resistance conductor. The inner end of the terminal is held centrally of the sheath by spacing Washer 16. Although only one end of the heating element is shown in detail, it will be'understood that the opposite end is assembled in a similar manner except that a solid washer will be used in place of'the star washer. In securing the terminals in place the resistance conductor is stretched to separate its turns.

The assembled unit is now placed in a suitable vibrating machine with the end provided with the star washer uppermost, and the sheath filled with a suitable powdered heat refractory insulating material 21, such as magnesium oxide, through the openings in t-he star Washer. During the filling operation the sheath is vibrated to distribute the powdered insulating material uniformly in the sheath and compact it somewhat by shaking the particles together. It will be observed that the insulating material is free to pass around the sides of spacing washers 16 and between the turns of the resistance conductor. After the sheath has been filled with insulating material, a solid washer 22 is inserted over the star washer 19 so as to close the sheath, and the ends of the sheath pinched or-bent over to hold the washers in place. The entire unit isnow subjectedto a swaging process for the purpose of com- .pacting the insulating material to a solid dense mass.

This swaging operation reduces the diameter of the unit and also slightly increases its length.

eferring to Fig. 4, after the unit has been s'waged, it is cut off at each end to'remove the washers and the grooved ends of the terminals, and the sheath'cut back at eachend .so as to expose a short length of the terminal 10. The exposed end of the terminal is now provided with nicks 25 on opposite sides, which may be cut or other wise formed, and an insulating washer 26 placed over the terminal. This insulating washer is preferably treated with "china wood oil or other material to keep out the moisture. A cylindrical metallic conducting lug 27 (Fig. 5) made of a suitably soft inaterial, such as brass, is next placed on the end of the terminal and seated against the washer 26. The lug has a diameter approximately equal to or slightly less than the outside diameter of the sheath and is provided with a central recess 28 into which the nicked portion of the terminal fits; By

a moisture proof seal for the end of the.

heating unit. A narrow circular rim 29 is left on the lug adjacent sealing washer 26 so as to more eil'ectively secure the Washer in place. In order to limit the distortion of the lug in the opposite direction, an annular groove 30 is provided adjacent the threaded portion 31. .It will be understood that the terminal in the right hand end of the unit will be provided with a connecting lug and the unit sealed in a similar manner. Nuts 32 are provided on the threaded portions of the lugs whereby suitable leads 33 and 34. connected to a source of electrical supply, may be. conveniently connected thereto.

While I have described my invention as embodied in concrete form and as operating in a specific manner in accordance with the provisions of the patent statutes, it should be understood that I do not limit my invention thereto, since various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States, 1s:

1. An electric heating unit comprising a metallic terminal provided with a threaded portion, a sinuous resistance conductor secured to said terminal by screwing it on said threaded portion, and compacted insulating material embedding said terminal and resistance conductor. I

2. An electric heating unit comprising metallic terminals provided with threaded portions, a helical resistance conductor slightly smaller than said threaded portions secured to said terminals by screwing it on said threaded portions, and compacted insulating material embedding said terminals and resistance conductor.

3. An electric heating unit comprising a resistance conductor having a portion provided with nicks projecting from said sheath, and a connecting lu provided with a recess fitting over said nic ed portion and secured to said terminal by being forced into said nicks.

4. An electric heating unit comprising a metallic sheath, a resistance conductor embedded in a compacted mass of insulating material in said sheath, a terminal for said resistance conductor having a portion provided with nicks projecting from said sheath, an insulating Washer surrounding said terminal closing the end of said sheath, and a connecting lug provided with a .recess fitting over said nicked portion, said lug being compressed so as to be forced into said nicks to secure it to said terminal and against said insulating washer to seal the unit.

5. The method of securing a terminal to a helical resistance conductor which consists in threading a portion of said terminal and screwing the resistance conductor on said threaded portion.

6. The method of securing a conducting lug to a terminal which consists in providing nicks on said terminal, placing an insu lating washer around said terminal so as to close said unit, roviding a recess in said lug, placing'said u over said nicked portion inst said was er, and then compressing said lug to force the material into said nicks and tightly against said insulating washer.

In witness whereof, I have hereunto set my hand this 29th day of March, 1922.

' CHARLES C. ABBOTT. 4 

